Process of making lead oxid.



llniirnn ferns AMBROSE G. FELL, OF NEW YORK, N. Y.

PRCCESS OF MAKING LEAD OXID.

SPECIFICATION formingpart of Letters Patent N 0. 674,031, dated May 14,1901.

Application filed March 30, 1900. Serial No. 10.844. (No specimens.)

To all whom it may concern:

Be it known that I, AMBROSE G. FELL, a citizen of the United States,residing in the city, county, and State of New York, have inventedcertain new and useful Improvements in the Manufacture of Lead Oxid, ofwhich the following is a specification.

This invention relates to the treatment of lead ores and compounds oflead not ores, but of a similar composition, and has for its object toprovide a process whereby such ores and compounds may be commerciallytreated ata reasonable cost for the production-of lead oxid for use inthe arts and sodium sulfate where the lead ore or lead com pound treatedcontains sulfur, as is usually the case.

The several steps constituting the process which forms this inventionmay be briefly and broadly stated as follows:

First. The treatment of thelead ore or compound by means that will behereinafter described for rendering the resultant lead salt decomposableby an alkali.

Second. The treatment of the resultant salt of the first step with afree alkali and with the aid of heat for the conversion of as large apercentage of the lead as possible into oxid.

Third. The treatment of the resultant of the second step with water andheat to dissolve out the soluble salts and the separation of said saltsby crystallization or otherwise as a by-product.

Fourth. The treatment of the residue from the third step of the process,mainly lead oxid, with a hot aqueous solution of an alkali of sufficientstrength to dissolve the oxid, decanting or drawing off the solutionfrom the insoluble residue, and the separation of the oxid from saidsolution by crystallization.

As galena (native lead sulfid) is the most abundant source of lead, thetreatment of this ore according to the present invention will now bedescribed, premisin g that this description gives the preferred methodof treatment, which is subject to considerable variation withoutdeparting from my invention.

First step: In order to convert the galena into lead sulfate, it isfirst reduced to powder and then intimately mixed with a suitablequantity of some sufficiently refractory material, also in powder, suchas lead oxid, lime, magnesia, 8:0. This mixture is carefully heated withaccess of oxygen, so as to oxidize both the lead-and sulfur of the ore.This heating will convert the lead in the charge treated wholly orpartially into lead sulfate. The time required for effecting thisoperation will be only about one hour, and the temperature to which thecharge is subjected may vary from 600 to 750 Fahrenheit. It is preferredin this step of the process to employ as a sufficiently refractorymaterial for admixture with the galena about an equal quantity, byweight, of the impure lead oxid, such as is produced at one stage inthis process. This refractory material, mixed with the ore, servesmechanically to separate the particles of the sulfid and afford accessfor the oxygen from the air. It prevents agglomeration, it shortens thetime required for this treatment, and it also appears to act chemicallywhen lead oxid is used in first combining with the oxygen from the airand then imparting the oxygen to the sulfid. It also combines with aportion of the sulfuric acid produced, whereby the resultant of thetreatment is a basic lead sul-- fate in lieu of a neutral sulfate. Theformer is preferable for the subsequent treatment by this process.

Second step: The treatment of the ore as described in the first step ofthe process renders it decomposable by an alkali, and the second steprelates to such decomposition. The product of the first step is cooled,by preference,and dry caustic soda in powdered form is thoroughly mixedtherewith, the proportion of the alkali being about equal to itscombining equivalent with the sulfur of the sulfid treated, which forpractical operations would be about twenty-six pounds of thefinelypowdered caustic soda to one hundred pounds of crude galena, whichis the sulfid commonly treated. If the soda is not finely powdered, itis well to pass the whole mass through a mill which will serve both togrind and mix it. This mixture is submitted to heat, and the soda almostimmediately converts the oxidized sulfur compounds into lead oxid andsodium sulfate; but in practice the mass is preferably stirred for aboutthirty minutes after being submitted to heat. The decomposition whichfollows the addition of the alkali will be furthered or accelerated bythe presence of the elements of water. This addition can be effected byintroducing steam into the mass during the oxidation of the leadcompounds, or the alkali may be moistened with water or steam. Theemployment of steam or water, as described, is not, however, necessaryto the operation.

Third'step: The product of the second step, which is mainly lead oxidmixed with some undecom posed ore, matrix, and the sodium sulfate formedby the combination of the sulfur and oxygen with the soda, is now putinto a suitable vesselsay an iron tank adapted to be heated withsteam-and water is added to dissolve out the soda salts therein. Thetemperature at which this is effected is not important. Stirringfacilitates the solution of the salts. The mixture is allowed to settleand the solution is decanted or drawn off from the insoluble residue andallowed to cool. If the solution be strong enough, the sodium sulfatewill crystallize out and forms a by-product of. the process. To avoidthe necessity of the concentration of the solution and to assure itsstrength, a solution of sodium sulfate may be employed in this-step inlieu of Water.

Fourth step: The undissolved residue remaining in the tank is nexttreated with a strong solution of caustic alkali, preferably soda. Inpractice this solution is made by dissolving one hundred pounds ofcaustic soda in about two hundred pounds of water. The solution used.should contain an amount of soda equal to three or four times that ofthe weight of thelead oxid contained in the mixture under treatment; butconsiderable variation in the strength of the solution is permissible.If it be too weak, the oxid will not precipitate on cooling and thesolution will require concentration. Potash or other caustic alkali maybe employed in lieu of soda; but as soda is satisfactory and affords amarketable by-product it is preferred. The mixture is heated to aboutthe boilingpoint, and the mass therein will be stirred, by preference.All of the lead oxid will be dissolved, and after this is effected thesteam is shut off and the 'undissolved matter allowed to settle. Theclear solution of lead oxid is now drawn off into a vessel containingmetallic lead in such form as to present as much surface as possible.granulated or sponged lead,formed by pouring molten lead into water, isemployed. The hot solution of lead oxid is allowedto remain in thisvessel in contact with the metallic lead for a short time and is thendrawn off into another vessel to cool, and as it cools it deposits'theoxid in the form of crystals. These latter will vary somewhat in sizeand color, according to the strength and volume of the solution and thetime taken up in cooling. When the cool and clear solution of soda isdrawn off from the oxid, the latter is Washed to free it from alkali,dried, and is then ready for use in'the arts.

The solution of the caustic soda employed In practice 1 for dissolvingout the lead oxid may be used almost indefinitely with very little loss;but the submission of the solution while hot to contact with metalliclead constitutes a very important feature of the process, as itpreserves the usefulness of the soda solution a permanent solvent of thelead oxid and secures the production of a pure lead protoxid instead ofa mixture of various oxids. Ordinarily a caustic soda solution may beemployed with good results four or five times only as a solvent of theoxid, after which it loses its solvent property. Presumably this isdue'to its having become gradually surcharged with an oxid richer inoxygen than the protoxid. This higher oxid will be only sparinglyprecipitated on cooling the solution, and its presence in quantityprevents the dissolving of the protoxid, which latter precipitates muchmore readily. To obviate the great loss of soda which such a conditionof the soda solution would entail, the hot solution before theprecipitation of the protoxid is filtered through or put in contact withthe spongy lead, as before described. The action of the metallic lead isto reduce the higher oxids, such as peroxid and red lead, to protoxidsby combining with their excess of oxygen. Thus the lead oxids arepractically all precipitated and the usefulness of the soda solution asa solvent is permanently maintained.

The sponged lead may be placed as a filtering material in asteam-jacketed tank and the hot solution be passed through the said tankon its way to the cooling and precipitating vessel. By this arrangementthesponged lead may serve as a mechanical filter also.

It is not.important that the soda or other alkaline solvent shall bepureor free from admixture with other s-ubstances,such as the sulfates,chlorids, and carbonates-of the alkali employed. So long as thereisenough of the free caustic alkali present to efiect the solution ofthe lead oxid it will suffice. Thus it follows that instead of employingthe commercial cautic soda the carbonate, as sodaash, may be employed,and by treatment of this with lime in a known wayit may be renderedcaustic wholly or in part and will thus serve the purposes required inthis process.

The first step of thisprocess, as described, is much preferred over theordinary'slowand expensive mode of roasting the lead ore; but

nevertheless the old or known mode of roasting maybe used in connectionwith the last three steps of this process, although not of course tosuch good advantage'nor with such good results. It will beunderstoodthat the term refractory as applied to the material mixed withthe lead compound in the first step of the process is relative and meansonly sufficiently refractory for the purpose. The

lead oxid, for example, is sufficiently refractory to resist the heatemployed.

Native lead sulfate may be treated by this process, in which case thefirst step would obviously be omitted, or native lead carbonate may betreated in the same manner asthe sulfate, in which case, however, thesalt of the alkali produced would be a carbonate instead of a sulfate.

Having thus described my invention, I claim 1. The herein-describedprocess of treating lead ore orsimilarlead compounds, which consists infirst converting the lead into a lead salt decomposable with an alkali,then treating the mass with an alkali to convert the lead into oxid,then dissolving out the soluble salts of the alkali, then heating theresidue containing lead oxid with a solution of alkali to dissolve thelead oxid, and then cooling said solution to allow the oxid tocrystallize out.

2. The herein-described process of treating lead sulfid, which consistsin first converting the sulfid into a lead salt decomposable with analkali, then mixing the mass with finelypowdered alkali, then heatingthe mixture to convert the lead into oxid, then dissolving out thesulfate of the alkali from the mass, and finally treating the residuewith a solution of caustic alkali to dissolve and remove the lead oxid,substantially as set forth.

3. The herein-described process, which consists in heating a masscontaining lead oxids with a solution of caustic alkali to dissolve theoxids, then reducing the higher oxids in the solution to protoxid, andthen separating the protoxid, substantially as set forth.

4. The herein-described process of treating a mass containing lead oxid,which consists in heating the mass with a solution of caustic alkali todissolve the oxid, then, while hot, putting said solution in contactwith metallic lead to decompose the higher oxids, and then cooling thesolution to permit the oxid to crystallize out, substantially as setforth.

5. The herein-described process of treating lead sulfid, which consistsin mixing the powdered sulfid with a powdered suitably refractorymaterial and heating the mass with access of oxygen to convert thesulfid into sulfate, then heating the mass with soda to convert the leadinto oxid, then dissolving out the sodium sulfate, then heating theresidue, containing lead oxid, with an alkaline solution to dissolve thelead oxid, then cooling said solution to allow the oxid to crystallizeout, and then drying the oxid, substantially as set forth.

6. The herein-described process of treating lead sulfid, which consistsin mixing the powdered suliid with a powdered suitably refractorymaterial and heating the mass with access of oxygen to convert thesullid into sulfate, then heating the mass with an alkali to convert thelead into oxid, then dissolving out the sulfate of the alkali, thenheating the residue, containing lead oxid, with an alkaline solution todissolve the lead oxid, then cooling said solution to allow the oxid tocrystallize out, and then drying the oxid, substantially as set forth.

7. The herein-described method of treating lead sulfid, which consistsin mixing it with lead oxid, both in pulverized form, then heating themass with access of oxygen, to convert the lead of the sulfid intosulfate, then heating the mass with an alkali to convert the sulfateinto oxid, then dissolving out the sulfate of the alkali, and thendissolving out the lead oxid, substantially as set forth.

In witness whereof I have hereunto signed my name, this 29th day ofMarch, 1900, in the presence of two subscribing witnesses.

AMBROSE G. FELL.

Witnesses:

THOMAS M. FELL, PETER A. Ross.

